This application represents a multidisciplinary, multi-institution response to RFA-DE-10-004: Increasing the Service Life of Dental Resin Composites (R01). The primary reasons for replacement of dental composites are caries and fracture. Whereas the mechanisms underlying both are ill-defined, the time course of years preceding most failures suggests that some process of degradation of the material/tooth interface and/or material occurs within the oral environment. Our overall goal is to further elucidate the mechanism of recurrent demineralization of tooth structure by bacteria around dental composite restorations, and to develop solutions for inhibiting it. To do this, we will identify conditions under which bacteria colonize interfaces between dental composite restoratives and tooth structure, by varying the starting size of the interfacial gap as well as the extent of cure of the resin composite. We further intend to evaluate the effect of the exposure to bacteria under cyclic loading on the marginal interface. A central hypothesis to be tested in this study is that there is a finite interfacial gap size that predisposes the composite restorative interface to colonization by bacteria and extensive demineralization, and that this interface may be further degraded by the effects of the bacteria. We also intend to incorporate a novel bioactive glass (BAG) into the resin composite to develop a new dental restorative material. Our hypothesis is that materials with BAG, and the interface between these materials and tooth structure, will undergo less chemical and mechanical degradation than those without an antibacterial bioactive glass when exposed to a combination of fatigue loading and oral-type biofilm formation for extended periods of time. To further probe the mechanism of failure, the anti-microbial behavior of the materials will be varied by producing resins with different extents of cure, which likely reflects the highly variable outcomes produced for dental composites in clinical practice. Materials will be placed into preparations in teeth and biofilms will be grown on their surface before and during intermittent fatigue loading of the interface. Interfacial failure and bacterial presence will be assessed by optical and scanning electron microscopy. Evidence of demineralization will be determined by energy dispersive spectroscopic (EDS) x-ray analysis. Evidence for biofilm effects on composites with and without BAG will be assessed by surface analysis, including gloss, surface roughness and microhardness. This application is particularly responsive to three aspects of the defined scope of the RFA, including development of new materials to confer caries resistance, determining whether the marginal gap size has an effect on bacterial colonization and further demineralization, and elucidating mechanisms of restorative material failure in a clinically relevant environment. The potential beneficial outcome of this work is extensive cost savings in oral health care and reduced oral pain in the US (and globally) due to longer lasting dental resin composite restorations.